Forces (C4) Flashcards
SI newton
kgms^(-2) from F=ma
Define mass
A measure of the amount of matter in something
Define weight
The force with which gravity pulls
Where does weight act from
the centre of mass
What is the centre of mass
mean position of mass, centre of gravity
method of finding a centre of mass
Push in no gravitational field until no turning moments are introdruced
What can a plumb line do
Find the centre of gravity by hanging the object
What is a free body diagram
one that isolates one object and just labels all the forces acting on it
Name some classic free body forces (5)
Weight Friction Drag Upthrust Normal contact force (reaction) Tension
What do all free body diagrams need?
Labelled arrows (scaled)
What is drag?
Frictional force in a fluid
What determines drag?
Cross sectional area shape speed texture of object density of fluid
Drag is proportional to
speed squared
What equation calculates net force?
F=ma
What is the principle of moments?
If the sums of the clockwise and anticlockwise moments are equal then the object is in rotational equilibrium
What is it called when there are no net linear forces?
translational equilibrium
What is a couple?
Pair of antiparallel forces that cause the object to spin without translational equilibrium as the forces are equal
What is the moment of a couple called
torque
What does the moment of a couple equal?
single Force times distance between them
SI unit for density?
kg/m^3
What is pressure measured in?
pascals
How do fluids exert forces on a submerged objects
perpendicular to the surface
and increases with depth
upthrust equals?
weight of the water displaced?
What is neutral buoynacy?
When a submerged object has the same density so doesn’t float or sink
